(1) Field of the Invention
The present invention relates to the testing of footwear and particularly to the evaluation of characteristics such as water repellency and cold intrusion of footwear. More specifically, this invention is directed to a footwear testing device capable of simulating the kinematic action of a walking individual under various environmental conditions. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
The science of footwear research undoubtedly dates from the beginning of man's use of animal skins and other materials for foot protection. As different materials were tried and different methods of attaching them to the feet were developed, differences in performance were observed. Those materials and designs which proved to be the most comfortable and convenient, and provided the best protection, were studied, copied and improved upon. This technique of making and subsequently testing prototypes is, as will be explained in greater detail below, still widely used. Thus, considering the testing of footwear for use by military personnel, until recently much of the testing was performed by volunteers under actual or simulated field conditions. This type of testing is costly, inaccurate with respect to some of the parameters of interest and not suitable for those tests, shock absorption capability for example, which could expose the wearer to the risk of injury.
Among the characteristics of footwear which desirably should be evaluated are water repellency, cold intrusion, sole and heel wear, heat-loss, and shock absorption. A high degree of moisture repellency is extremely important since dry footwear is more comfortable to the wearer and greatly reduces the incidence of many types of foot disorder. Similarly, the ability to keep the foot warm is a characteristic of importance. As is well known, cold injury to feet is a problem which has affected military campaigns throughout history. It is difficult to evaluate factors such as water repellancy and cold intrusion through the use of wear-type tests because of the subjective nature of such tests. For example, most individuals are unable to detect small amounts of moisture entering their footwear and when moisture is detected they are unable to provide an exact location.
Foot injuries are, of course, a serious problem in industry and in the military. Accordingly, footwear is continually being redesigned, tested and updated to include recent technological advances which provide additional protection. The tests to be performed include measurement of the cushioning/shock absorbing characteristics of the footwear and, as noted above, these characteristics can not be measured by wear-testing. In the prior art a "falling dart" test has frequently been used to measure the shock absorbing characteristics of a boot or shoe. These tests employ an impactor which is dropped onto the insole of the shoe and an accelerometer which measures the change in acceleration resulting from the impactor striking the shoe. Shoes are normally tested in the rear foot (heel) and forefoot (ball) areas. Such "falling dart" tests are not entirely satisfactory since they frequently necessitate cutting away part of the shoe under test in order to allow the impactor to enter and such removal of material from any structural portion of a boot or shoe will significantly alter is performance. Further, falling dart impactors are poor replicates of the human foot and, since shoes normally conform to the shape of the wearer's foot, a flat or hemispherical impactor may not provide an adequate presentation of the cushioning characteristics which would actually be experienced by the foot. Also, a "falling dart" test will only measure the characteristic of a new shoe and impact absorption is known to change as a result of use. It would be extremely desirable to have the means of determining how rapidly the degree of protection afforded by the footwear under test would deteriorate in actual use.
It has also been proposed to employ strain gages attached to the legs of an individual walking or running on a treadmill and/or transducers located in the shoe under test to test for shock absorption characteristics. The major disadvantages of these approaches is that they require the use of human subjects and highly skilled technicians both of which greatly increase the cost of testing.
The advantages incident to replacing wear-testing employing human volunteers with a machine are numerous and obvious. However, the mechanisms required to duplicate the movements of the human's foot during walking are quite complex. The human foot is compressed of twenty-six (26) separate bones wraped in a mixture of muscles, ligaments, fat and calluses. The duplication of such a complex structure would be nearly impossible. This fact has contributed to the prior failure to provide footwear testing equipment capable of measuring the parameters of interest, particularly under the extreme environmental conditions of interest, with a reasonable degree of accuracy.